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Week 9 discussion - Virtual Functions and Abstract Base...

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Virtual Functions and Abstract Base Classes Week 9
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Administrative Add/Drop with a “W” Deadline This Friday (11/12) Project 4 is available Due November 24
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A new class: Rectangle class Rectangle { private: int length; int width; string color; public: Rectangle(int l, int w, string c); int getArea(); int getPerimeter(); void setColor(string color); } class Square: public Rectangle { public: Square(int l, string c); int getArea(); int getPerimeter(); void setColor(string color); } //Implementation of getArea() multiplies length * length
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Square s; Rectangle *r = &s; Rectangle is a superclass of Square, so a pointer to a Rectangle can also point to a Square If we call r->getArea(), will it call Rectangle's implementation or Square's?
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Apparent vs. Actual Type Answer: Since C++ can't tell statically that r is actually a pointer to a Square, it uses the apparent type, so the implementation for Rectangle will be called. Next Question: How can we get C++ to determine the actual type at runtime?
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Virtual Functions Answer: Virtual functions!
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